Photovoltaic systems have become more prevalent as prices decrease. Most photovoltaic systems are grid-connected-only systems that offset electric utility costs. These grid-connected systems usually pay for themselves in ten to thirty years depending on the installation location and government subsidies offered at the time of installation.
Other photovoltaic systems which are currently less prevalent are used to create alternating current power in the absence of a connection to the utility. These stand-alone systems are used either to provide backup power or to power loads in a remote location. Stand-alone systems are usually expensive due to the need for battery storage and for the additional inverter costs associated with providing power to non-resistive loads. Furthermore, the batteries of such systems are heavy, not easily moved, and are designed to be used only inside the photovoltaic system.
Very small photovoltaic applications exist with or without batteries for the purpose of operating very small electronic devices such as solar calculators or cell phones. These systems are low in power and can only be used for a narrow range of low-power devices. Furthermore, the battery in such systems, if there is a battery, is dedicated to use in the photovoltaic system and cannot be easily used for other applications. Furthermore, these low power applications are designed only for stand-alone applications—the photovoltaic panel is wasted most of the time since the power it can produce most of the time is not needed for the intended load but also cannot be pushed into the grid to save electricity costs.
Conventional photovoltaic systems are not easily reconfigurable and often present safety or interconnection issues. For example, the battery of a conventional photovoltaic system cannot be removed for other applications while the photovoltaic panel continues to either source power into the utility grid or produce AC power without a utility grid present.